This research focusses on metal-catalyzed oxidative modification of biopolymers, especially of proteins. The reaction is enabled by the binding of a metal such as iron or copper to a cation binding site on the targeted protein. Oxygen reacts at that site to generate an activated species which then oxidizes amino acid residues at the binding site. This oxidation leads to an apparently irreversible, covalent modification of proteins which has been implicated in important physiologic and pathologic processes. These include the aging processes, arthritis, carcinogenesis, gene regulation, hypertension, intracellular protein turnover, oxygen toxicity, and reperfusion injury after ischemia. Determination of the actual roles of oxidative roles of oxidative modification in these processes requires the application of specific assays for modified proteins, identification of the structural and functional changes induced by modification, and understanding of factors which modulate the rate and specificity of oxidative modification in vivo. These are the current aims of this project. Emphasis was placed in the last year on the establishment of collaborative investigations designed to identify processes in which oxidative modification of proteins occurred. Correlations were observed in peritoneal fluid of mice during tumorigenesis induced by chronic inflammation; in the plasma of rats after exposure to ionizing radiation; in the tracheal secretions of prematurely born humans who were supported by mechanical ventilation; in the proteins of cultured endothelial cells exposed to oxidative stress; and in the human protease inhibitor, alpha-2- macroglobulin, which was functionally inactivated by exposure to neutrophils. As an outgrowth of such studies, it was found that low concentrations of copper were able to inactivate the protease from the human immunodeficiency virus. More detailed investigation of the inhibition established that it occurs at a site located on the surface of the enzyme, rather far from the active site. This finding suggests the possibility of developing a new class of protease inhibitors which are not directed to the substrate- binding site.